Low-sulfur article coated with a platinum-group metal and a ceramic layer, and its preparation

Abstract

A coated article is prepared by furnishing an article substrate having a free sulfur content of less than about 1 part per million. The low-sulfur article may be made of a material selected to have a low sulfur content, provided with a scavenging element that reacts with free sulfur to produce a sulfur compound, or desulfurized by contact with a reducing gas such as hydrogen. A platinum-group metal layer is deposited over the article substrate, and a ceramic coating is applied over the platinum-group metal layer.

What is claimed is:  
     
       1. A method for preparing a coated article, comprising the steps of: 
       furnishing an article substrate formed of a nickel-based superalloy and having a free sulfur content of less than about 1 part per million; depositing a layer of a platinum-group metal over the article substrate; and applying a ceramic coating over the layer of a platinum-group metal.  
     
     
       2. The method of  claim 1 , wherein the step of furnishing includes the step of 
       fabricating the article substrate from a material having a free sulfur content of less than about 1 part per million.  
     
     
       3. The method of  claim 1 , wherein the step of furnishing includes the step of 
       fabricating the article substrate from a material comprising a scavenger element that is reactive with free sulfur to form a sulfur-containing compound, the scavenger element being present in an amount sufficient to reduce a residual free sulfur content of the article substrate to less than about 1 part per million.  
     
     
       4. The method of  claim 3 , wherein the step of furnishing includes the step of 
       providing as the scavenger element an element selected from the group consisting of yttrium, hafnium, and zirconium.  
     
     
       5. The method of  claim 1 , wherein the step of depositing includes the step of 
       depositing a layer of platinum over the article substrate.  
     
     
       6. The method of  claim 1 , wherein the step of depositing includes the step of 
       depositing the layer of platinum-group metal to a thickness of from about 2 to about 10 micrometers over the article substrate.  
     
     
       7. The method of  claim 1 , wherein the step of applying includes the step of 
       applying a coating comprising yttria-stabilized zirconia over the layer of the platinum-group metal.  
     
     
       8. The method of  claim 1 , wherein the step of furnishing includes the step of 
       furnishing an article substrate which is a component of a gas turbine engine.  
     
     
       9. A coated article made by the process of  claim 1 . 
     
     
       10. A method for preparing a coated article, comprising the steps of: 
       furnishing an article substrate having a free sulfur content of less than about 1 part per million, wherein the step of furnishing includes the step of  
       providing the article substrate having more than about 1 part per million of free sulfur, and  
       processing the article substrate to reduce the free sulfur level to less than about 1 part per million, wherein the step of processing includes the step of contacting the article substrate to a reducing gas at elevated temperature;  
       depositing a layer of a platinum-group metal over the article substrate; and  
       applying a ceramic coating over the layer of a platinum-group metal.  
     
     
       11. The method of  claim 10 , wherein the step of contacting includes the step of 
       contacting the article substrate to a hydrogen-containing gas at elevated temperature.  
     
     
       12. A method for preparing a coated article, comprising the steps of: 
       furnishing an article substrate made of a nickel-base superalloy and having a local free sulfur content of less than about 1 part per million in a selected region;  
       depositing a platinum-group metal layer over the selected region of the article substrate; and  
       applying a ceramic coating over the platinum-group metal layer in the selected region of the article substrate.  
     
     
       13. A coated article made by the process of  claim 12 . 
     
     
       14. The method of  claim 12 , wherein the step of furnishing an article substrate includes the step of 
       furnishing an article substrate which is a component of a gas turbine engine.  
     
     
       15. A coated article, comprising: 
       an article substrate comprising a nickel-base superalloy and having a sulfur content of less than about 1 part per million;  
       a platinum-group metal layer overlying the article substrate; and  
       a ceramic coating overlying the platinum-group metal layer.  
     
     
       16. The article of  claim 15 , wherein the article substrate is a component of a gas turbine engine.